JPH10196637A - Conductive roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hardly cause a fog phenomenon and to keep a rectangular shape of a nip with ease by constructing a conductive rubber layer of a conductive ethylene propylene rubber, specifying its surface roughness, and forming a roller into a normal crown shape. SOLUTION: A conductive ethylene propylene rubber composition is mixed and kneaded, wound around the outer circumference of a steel core shaft 1 processed with a primer, and vulcanized in the inside of a cylindrical metal die so as to be formed into a conductive rubber layer 2. The conductive rubber layer 2 is ground and polished so that a roller surface roughness Rz ranging from 1μm to 7μm is provided. If the surface roughness Rz exceeds the predetermined range, deterioration in a degree of fog is caused, while the surface roughness Rz is lowered below the predetermined range, productivity is reduced. The roller is formed into a normal crown shape in which the central outside diameter is larger than the outside diameter of each longitudinal end part. As to the shape of the roller, a straight shape part, may be arranged in the center between taper parts in both ends, or a substantially spindle type shape, in which both ends and the center part are connected together by curved lines such as parabolas, may be used. In this way, a degree of fog can be lowered, while durability is improved, and a nip shape can be kept in a rectangular shape with ease.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive roller used as a charging roller, a developing roller or a transfer roller of a developing device in an electronic copying machine or a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, a plain paper copying machine of the electrophotographic type, that is, a so-called electronic copying machine, forms an electrostatic latent image on a photosensitive drum using a photosensitive member that generates electric charges by light, There is known a system in which a toner, which is a colored charged powder, is adhered to an electrostatic latent image to develop, that is, a visible image, and this is fixed on recording paper by heat. In forming an electrostatic latent image on the surface of the photoconductor drum, the surface of the photoconductor drum is charged in advance, and an original image is projected on the charged portion through an optical system to eliminate the charging of the portion that has been exposed to light. That is being done.

[0003] With the remarkable spread of copying machines in recent years, there has been an increasing demand for simplification of equipment, that is, reduction in cost and size. In order to respond to such demands, we are developing organic photoconductive materials as photoreceptors, adopting a simpler one-component non-magnetic development method with a mechanism as a development method, and a method of charging the surface of the photoreceptor drum, Improvements have been made in various directions, such as adoption of a contact roller charging method that makes it easier to reduce the size of the device than a conventional corona discharge method.

In this contact roller charging system, a conductive elastic roller is installed so that its surface is in contact with the surface of the photosensitive drum, and the surface of the photosensitive drum is charged by rotation of the roller. Also, a conductive elastic roller is often used as a cleaning roller. For such a conductive roller, it has a stable volume resistivity of about 10 ⁵ to 10 ¹² Ω · cm, has a suitable elasticity, has a small compression set and is unlikely to cause creep, Further, it is required that the photoconductor is not contaminated.

As a roller which can meet such a demand,
For example, a synthetic rubber material such as nitrile butadiene rubber (NBR) or silicone rubber is used, its volume resistivity and rubber hardness are adjusted to desired values, and a conductive elastic layer made of these rubber materials is provided on the outer periphery of the roller core shaft. Formed single-layer rollers are known. For rubber materials, usually the addition of a plasticizer or softener to reduce rubber hardness,
In order to adjust the conductivity, mixing of a conductive powder such as carbon black is performed.

[0006]

In such a conductive roller, various improvements have been made in the material and the shape thereof in order to further reduce the price and size of the device. For example, as a rubber material, ethylene propylene rubber (EPM or EPDM), which easily obtains low hardness, has excellent weather resistance, and is advantageous in terms of price, has attracted attention, and the roller has been reduced in diameter.

[0007] However, with these improvements, new problems have to be solved. For example, when a conductive roller is manufactured using ethylene propylene rubber as a rubber material and used as a developing roller, a phenomenon called “fog” in which toner scatters on a white background portion of an image is compared with silicone rubber. It has been found to be easy to happen. Therefore, there is a demand for a conductive roller that does not easily cause fogging even when ethylene propylene rubber is used as the material.

It is effective to reduce the diameter of the core shaft in response to the reduction in the diameter of the roller. However, when the diameter of the core shaft is reduced, the core shaft is pressed against a photosensitive drum or another roller. In this case, there is also a problem that the core shaft is easily bent with respect to the pressing load imposed on both ends. When such deflection occurs in the conductive roller pressed against the photosensitive drum, the pressure at which the roller is pressed against the photosensitive drum becomes uneven in the nip area (the contact area between the photosensitive drum and the roller). It is also known that the photoreceptor drum in a portion to which a large load is applied is locally scraped and worn or damaged when the roller rotates, thereby reducing the durability of the photoreceptor drum and the roller.

Incidentally, such damage to the photosensitive drum is caused by
Even if the core shaft does not bend, it also occurs when the outer diameter differs between the end portion and the center portion in the length direction of the core shaft or the linearity is easily impaired due to the molding method of the roller. For example, when a roller is manufactured by casting and curing liquid silicone rubber in a mold using liquid silicone rubber as the rubber material, it is not insignificant when the temperature is returned to room temperature after demolding due to mold temperature unevenness during curing. Despite this, rollers are often warped. In the case of a roller with a grinding finish, the rubber expands thermally during polishing so that dimensional accuracy is not easily obtained, and the outer diameter of the shaft end is liable to be larger than that of the central portion because the rubber escapes. This is particularly remarkable in a roller having a small diameter in which the rubber hardness is often set low.

By the way, when the degree of deflection seen on the core shaft during the pressing is increased, the center of the core is lifted from the surface of the photoreceptor drum to be pressed, and usually has a rectangular shape having a long roller length. The shape of the nip area becomes a drum shape with a constricted central part, and the nip width becomes uneven,
There are inconveniences such as unevenness in the obtained image. Therefore, there is a demand for a conductive roller which can easily maintain a nip shape in a shape close to a rectangle even when the core shaft is reduced in size in order to promote downsizing, and which does not cause abrasion of the photosensitive drum.

In view of the above circumstances, the present invention has a possibility that the nip shape can be easily maintained in a shape close to a rectangle and the photoreceptor can be shaved so that even when ethylene propylene rubber is used as the rubber material, the apparatus can be further downsized. It is an object of the present invention to provide an excellent conductive roller having a small number of conductive rollers.

[0012]

As a result of extensive studies for the above purpose, it has been found that the occurrence of the fogging phenomenon is influenced by the outer diameter of the roller and its surface roughness. That is, fogging is less likely to occur when the outer diameter of the roller is increased, but the upper limit of the outer diameter of the roller cannot be increased because the upper limit is determined by the magnitude of the rotational torque of the apparatus. Increasing the roller outer diameter goes against the miniaturization of the apparatus. Accordingly, the present invention provides a method for producing a roller having a surface roughness R without increasing the outer diameter of the roller and without changing the type or composition of the rubber material composition.
The inventors have found that by maintaining z in a specific numerical range and devising the shape, the roller hardly causes a fogging phenomenon and the nip shape can be easily maintained in a rectangular shape.

That is, the conductive roller of the present invention is a conductive roller having a conductive rubber layer formed on the outer periphery of a core shaft, wherein the conductive rubber layer is made of conductive ethylene propylene rubber and has a surface roughness Rz. It is characterized in that it has a regular crown shape in which the outer diameter at the center is larger than the outer diameter at both ends of the roller within the range of 1 to 7 μm.

The conductive rubber layer has a positive crown of 0.03 to 0.5 mm represented by the difference (φ ₂ −φ ₁ ) between the center outer diameter φ ₂ and the end outer diameter φ _1. The crown shape is a further feature.

In the conductive roller of the present invention, the surface roughness Rz of the roller is preferably 7 μm or less,
More preferably, it is in the range of 2 to 4 μm. Surface roughness Rz
Exceeds 7 μm, the degree of fogging deteriorates, which is not preferred. On the other hand, in order to make Rz smaller than 1 μm, a special step or the like is required, and the productivity is reduced. Therefore, in the present invention, the surface roughness Rz of the roller
Is preferably 1 μm or more.

In the present invention, the regular crown shape that defines the roller in combination with the surface roughness Rz in the above range indicates that the central portion has a larger outer diameter than the outer diameters at both ends in the longitudinal direction of the core shaft, and has a middle height. For example, as shown in a side view in the longitudinal direction of the roller shown in FIG. 1A, there may be a straight portion at the center between tapered portions at both ends, or a side surface shown in FIG. As shown in (2), the appearance in which both ends and the center are connected by a curve such as a parabola may have a substantially spindle shape. In the following description, the type of crown shape shown in FIG. 1A is referred to as type A, and the type of crown shape shown in FIG.

In the present invention, the crown amount is 0.03 m
If it is less than m, the nip width at the center becomes smaller than the both ends, as in the case of the straight roller, and the nip shape tends to be wrapped, and the fogging phenomenon increases, which is not preferable. On the other hand, the crown amount is 0.5m
If it is larger than m, the pressure at the center of the roller at the time of press contact becomes too large compared to the both ends, and the nip width at the center becomes larger than the both ends, and the nip shape becomes closer to a drum shape. Absent. That is, the crown amount of the roller that easily keeps the nip shape close to a rectangle is preferably in the range of 0.03 to 0.5 mm, and more preferably in the range of 0.1 to 0.3 mm. In the conductive roller of the present invention, the conductive ethylene propylene rubber of the present invention desirably has a rubber hardness of 50 to 70 °.

Further, the conductive roller according to the present invention is a conductive roller in which a conductive rubber layer is formed on the outer periphery of a core shaft, wherein the core shaft has a regular crown shape having an outer diameter at a central portion larger than an outer diameter at both ends. It is characterized by being. As a core shaft, by using a positive crown shape having a central portion outer diameter larger than both end outer diameters, even if the roller outer diameter is reduced, the nip shape is kept closer to a rectangular shape. Can be

The conductive roller of the present invention can be manufactured according to a general method of manufacturing a silicone rubber roller. For example, after the conductive rubber composition of the present invention is wound around the outer periphery of a roller core shaft, it is housed in a cylindrical mold and heated and pressurized for vulcanization, or a cylindrical mold in which a roller core shaft is attached in advance. After a rubber layer is formed on the outer periphery of the core shaft by various methods such as injection molding or extrusion using the same, it may be ground and polished so as to have a shape according to the present invention.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 A conductive ethylene propylene rubber composition (Showa Electric Wire & Cable Co., Ltd. compound name: 9582R) was kneaded and wound around the outer periphery of a primer-treated iron core shaft (body length 310 mm, outer diameter φ10 mm), and then placed in a cylindrical mold. 5m thick after vulcanization with
m of a conductive ethylene propylene rubber layer was formed.

Then, the obtained straight-shaped roller is polished to a diameter of 20.5 mm at the center and 20.0 mm at both ends.
mm (crown amount 0.5 mm), type of crown shape type A (the length of the tapered portions at both ends is 50 m each)
m), a conductive roller of the present invention having a surface roughness Rz of 2 to 3 μm was produced.

The obtained roller was mounted on an actual machine, and the degree of fogging and the durability were evaluated. The degree of fogging is expressed as the number of toners found per 1 mm ² of a white background portion of the chart after passing, and is as small as eight, and the durability is good enough to be copied until the toner runs out. Met. In the case of the current silicone rubber roller, the number is about 10 or less.

Examples 2 to 4 A conductive roller of the present invention was manufactured in the same manner as in Example 1 except that the center diameter, both end diameters, and the type of crown shape of the roller were changed within the scope of the present invention. did. Also in these examples, the degree of fog and durability were evaluated in the same manner as in Example 1. The results of these evaluations are shown in Table 1 below.

[0024]

[Table 1] Comparative Examples 1 to 8 Next, as comparative examples, straight rollers made of the same conductive ethylene propylene rubber composition as the rollers of these examples were manufactured, and the degree of fogging and durability were similarly evaluated. The evaluation results are shown in Table 2 below.

[0025]

[Table 2] Comparative Examples 9 to 12 Further, a roller made of the same rubber composition and having a surface roughness outside the range of the present invention was manufactured, and the degree of fogging and durability were similarly evaluated. The results of these evaluations are shown in Table 3 below.
Shown in

[0026]

[Table 3] As is clear from Tables 1, 2, and 3, the roller of the comparative example has a large degree of fogging of 15 to 120, and is considered to be difficult to use as a replacement for the current silicone rubber roller. The rollers of Examples 1 to 4 have a low fogging degree of 8 to 11 and have good durability so that copying can be performed until toner is almost exhausted. Was.

[0027]

As described above, according to the present invention, even when ethylene propylene rubber is used as the rubber material, a conductive roller having a low degree of fogging and excellent durability can be obtained. Further, it is possible to provide an excellent conductive roller which can easily maintain the nip shape in a shape close to a rectangle and can reduce the possibility of damaging the photosensitive drum so that the developing device can be downsized.

[Brief description of the drawings]

FIG. 1 is a schematic side view in the length direction of a roller showing an example of a crown shape of the present invention.

[Description of Signs] 1 ... Roller core shaft 2 ... Conductive rubber layer

Claims (3)

[Claims] 1. A conductive roller having a conductive rubber layer formed on an outer periphery of a core shaft, wherein the conductive rubber layer is made of conductive ethylene propylene rubber and has a surface roughness Rz of 1 to 7 μm.
A conductive roller having a regular crown shape in which the outer diameter at the center is larger than the outer diameter at both ends of the roller within the range of m. 2. The method according to claim 1, wherein the conductive rubber layer has a positive and negative crown amount of 0.03 to 0.5 mm represented by a difference (φ ₂ −φ ₁ ) between a center outer diameter φ ₂ and both end outer diameters φ _1. The conductive roller according to claim 1, wherein the conductive roller has a crown shape. 3. A conductive roller in which a conductive rubber layer is formed on the outer periphery of a core shaft, wherein the core shaft has a regular crown shape whose outer diameter at a central portion is larger than outer diameters at both ends. Sex roller.